High temperature mechanical fluid compositions



United States Patent Ofiice 3,026,263 Patented Mar. 20, 1962 3,026,263 HIGH TEMPERATURE MECHANICAL FLUID COMPOSITIONS Fred S. Arimoto, 'Newark, Del., assignor to 'E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Mar. 5, 1959, Ser. No. 797,326 4 Claims. (Cl. 252-50) This invention is directed to improved antioxidant compositions for use in mechanical fluids at elevated temperatures; and, more particularly, an N-aryl-Z-naphthylamine or an acridine in combination with selected polynuclear aromatic hydrocarbons as a stabilizing agent. Mechanical fluids are those fluids adaptable for use as lubricants, heat transfer agents, power transmission agents, hydraulic fluids and the like. The polynuclear aromatic hydrocarbons are selected from the group that has at least three fused rings and a singlet-triplet excitation energy less than 20,000 cm.- and are represented by such compounds as anthracene, benzanthracene, chrysene, pyrene. The singlet-triplet excitation energy for a number of aromatic hydrocarbons is given in the Journal of the American Chemical Society, vol. 77, page 1949 (1955). This invention also deals with the stabilization of mechanical fluids against the deleterious effects of heat and oxygen at elevated temperatures.

Untreated mechanical fluids, such as the esters and silicone oils, that are adapted for use at 300 F. and above absorb oxygen at these elevated temperatures and undergo undesirable changes. The combination of heat and oxygen, for example, causes the fluids to undergo an increase in viscosity. In some fluids, however, the viscosity may decrease which is also undesirable. These oxidized fluids may become corrosive to metals. This condition limits the kinds of metal that may be used in contact with the fluid and may cause failure or troublesome operation of such metal parts. The deposition of sludge is another condition that arises when these fluids are subjected to thermal and oxidative stresses.

Numerous stabilizing agents have been applied to overcome or to suppress the changes encountered in mechanical fluids at elevated temperatures. Many of the agents have a stabilizing action at mildly elevated temperatures; but above 300 F. and particularly around 500 F., agents that are stabilizers at lower temperatures may lose their effectiveness, actually promote oxidation and become prooxidants. One such agent is phenothiazine. Phenothiazine is commonly used as an antioxidant in synthetic lubricants designed for use at high temperatures in aircraft gas turbines. Its usefulness, however, is limited because at about 400 F., and at higher temperatures, phenothiazine accelerates oxidation thereby promoting the degradation of the lubricant and causing heavy amounts of sludge to form.

It is an object of the present invention to provide novel stabilizing agents that are eifective, at elevated temperatures, to retard undesirable changes a mechanical fluid may undergo on exposure to heat and oxygen; the changes retarded include a change in viscosity, the formation and deposition of sludge and the development of corrosive action on metals. it is another object of this invention to inhibit the oxygen absorption of mechanical fluids at elevated temperatures. It is a further object of this invention to improve the stability of mechanical fluids so that said fluids, when utilized at high temperatures, reflect a minimum change in viscosity, a minimum corroding of metals, and a'minimum deposition of sludge. These objects are achieved by treating the mechanical fluid with a small amount of an acridine or an N-aryl-Z-naphthylamine in combination with a small amount of a polynuclear hydrocarbon such as anthracene, chrysene, or pyrcne; a synergistic effect is achieved in this combination of agents. These and other objects will become apparent in the following description and claims.

More specifically, the present invention is directed to a mechanical fluid for use at 300 F. and above, said fluid containing an antioxidant composition of an N-aryl-2- naphthylamine or an acridine and a polynuclear aromatic hydrocarbon having at least three fused rings and whose singlet-triplet excitation energy is less than 20,- 000 cmr- This invention contemplates a mechanical fluid containing one of the described and claimed novel combinations of antioxidants in an amount within the range of 0.025% to 2.5% by weight of fluid for each component of said combination.

Mechanical fluids suitable for use as lubricants may be the ester or silicone oil type represented by bis(2-ethylhexyl)sebacate, tetrabutyl pyromellitate, tetrakis (1H,1H, wH-polyfluoroalkyl) pyromellitate (alkyl=C and C pentaerythritol tetrapivalate, and DC-550 silicone oil. The lubricant must be adapted for use at elevated temperatures; that is, it must have a low vapor pressure and be stable enough with the protection that the combinations of stabilizing agents provide to be used at temperatures in the range of 500 F.

The synergistic combinations of the antioxidants of this invention are specific in their effectiveness as illustrated in Table I and are particularly valuable for protecting fluids of the ester and silicone oil types against the damaging effects of heat and oxygen at temperatures from 300 F. and above. These temperatures are commonly encountered in the ester type lubricants used in the bearings of gas turbine engines and may be reached by the ester compounds used as hydraulic fluids. Representative combinations of agents that exhibit significant synergism are acridine and pyrene, anthracene and N-phenyl-Z-naphthylamine, and N-phenyl-Z-naphthylamine and pyrene. The preferred combination is acridine and pyrene.

To illustrate the improvement of the esters and silicone oils in their resistance to oxygen absorption and to viscosity change and in the reduction of their corrosion of metals at elevated temperatures, the following examples of the marked effect of the combinations of selected stabilizing agents are given. The examples are preceded by a description of the test apparatus and procedure, and part of the test results are presented in tables.

In determining the effect of heat and oxygen at elevated temperatures on mechanical fluids, and, measuring the stabilizing action of antioxidants under these conditions, a 20 mm. glass tube of 25 ml. capacity, rounded on the bottom and sealed at the top with a ground glass joint, was utilized. The glass joint bears a 5 mm. open glass tube that extends almost to the bottom of a 20 mm. tube or oxidation cell; from the glass joint also extends a side outlet tube; this side outlet tube is connected in series with a U-tube containing anhydrous calcium sulfate as a Water-absorbent material, a U-tube containing asbestos flakes impregnated with sodium hydroxide as a carbon dioxide absorbent material, an acetone/solid carbon dioxide trap for condensing volatile oxidation products, a small pump to circulate oxygen in the closed system, and a rotameter to measure the rate of flow of oxygen. A gas burette of oxygen and thermobarometer to compensate for temperature and pressure changes are connected in series with each other and as a side branch to the oxygen absorption system.

To measure the oxidation of a mechanical fluid, the effects of heat and oxygen on the fluid, and the stabilizing efiect of an agent or combination of agents, a ml. or m1. sample of'fiuid, with and Without an added agent to be tested, is placed in the oxidation cell and the cell connected to the assembled apparatus through the ground glass joint. The burette is filled with oxygen, and the system temporarily open to the air through a stop-cock is flushed with oxygen. ing if the system will maintain a pressure of 10 to 20 mm. of mercury above that of the atmosphere for five minutes without change) and being sure there are none the oxygen pressure is equalized to that of the atmosphere. The pump is started, and the oxygen flow is set at mL/min. by adjusting the stopcock on the outlet side of the pump. A Woods metal bath at the desired temperature, say 500 F., is raised around the oxidation cell. The oxygen After testing for leaks (by observlowing examples, substantially the same effectiveness being achieved.

The following represent preferred combinations of the antioxidants of the present invention:

N-phenyl-Z-naphthylamine with anthracene N-phenyl-Z-naphthylamine with pyrene N-phenyl-Z-naphthylamine with chrysene Acridine with anthracene Acridine With chrysene Acridine with pyrene EXAMPLE 1 The effect on the rate of oxygen absorption by bis(2- ethylhexyl) .sebacate and on its viscosity increase in three hours at 500 F. in the absenceand presence of selected "antioxidantsand-combinations ofantioxidants isshown in Table I.

Table I OXIDATION OF ,BIS(2-E.THYLHEXYL) SEBACATE [20 ml. sample at 500 F., oxygen at 25 1111./Illi11.]

Viscosity Total Relative Oxi- Increase in Oxygen Absorbed Oxygen dation Rate percent Amt Pereent Ave, for Ave. for Abmeasured No. Agent Tested by'Weight lst'hr. 3rd hr. sot-bed at F.

mL/rnin. ml./1nin. 1n 3{1rs.

1st 2nd 100 210 hr. 111.

None 3.17 1. as 456 1 1 22 2s Acridine 0.5 2.05 1. 30 308 0.65 0.73 Anthracene..- 0.5 2. 29 1. 62 395 .75 .87 27 26 Chrysene 0.5 3.40 2.48 513 1.07 1.34 17 s N-Phenybznaphthylumiue 0.5 2. 00 1.68 369 .82 90 27 27 Pyrene 0.5 2.86 2. 47 460 .90 1 as 1s 2s Acridine anthrac 0. 25+0. 25 1. 37 .71 186 .43 Aeridine DYrene- 0. 025+0.o25 2. 33 1.59 344 .74 Acridine pwene-.- 0 05+0. 05 1. 00 0.71 188 .31 Acridine pyrene 2. 5+2. 5 2. 21 1.45 335 .70 Anthracene N-phenyl-fZ-napht'nyl- 0. 25+0. 25 1.71 1. 33 262 .54

armne. Ohryseue N-phenyl-2-naphthyl- 0. 25-1-0. 25 2.04 1.33 298 .64 .71 11 19 am 1'19. N-ph enyl-2-naphthylamine pyrene. 0.25+0.25 1. 69 1.30 292 53 .70 14 21 burette is read every five minutes for three hours. The The combinations of acridine and anthracene (No. 7), burette is refilled with oxygen as necessary through a stopacridine and pyrene (particularly No. 8b) anthracene cock. To measure the viscosity change in a fluid under 55 and N-phenyl-Z-naphthylamine (No. 9), chrysene and N. the test conditions, the material before and after oxidaphenyl-Z-naphthylamine (No. .10), and N-phenyl-Z-naphtion is permitted to flow through a calibrated modified thylamine and pyrene (No. 11) markedly retard the rate Ostwald viscosimeter (ASTM procedure D445-46T). To of oxidation of ,bis(2-ethylhexyl) sebacate and definitely determine the corrosive action of an oxidized fluid at elereduce its viscosity increase under these oxidizing condivated temperatures metal sheet or foil test pieces about one tions. Thus these combinations of agents are distinct inch square are immersed in the fluid to be oxidized and stabilizers for the ester at the elevated temperature. The measured for Weight loss after the test. same agents'used alone (Nos. 2, 3, 4, 5, 6) in an amount In the representative examples which follow, the followequal to th t f th total amo t of th ombin tion ing alkyl and benz SLlbStitUtfid acridine compounds as 3- stabilize the ester much less than when used in a proper methylacridine, 2,7-dimethylacridine, 2,4,5,7tetramethylcombination and may'actually promote oxidation, chrysac'ridine, benzEalacridine, lO-methylbenz[a]acridine, 8,9- ene, for example (No.4). dimethylbenzta] acridine, 8 9 12-trimeth lbenz[a] acridine,

3 PL benz[c]acr1d1ne, 9-methylbenzilclacnd1ne, and 10,].1-d1- EXAM E 2 methylbenz[c]acridine may be substituted for the acricline The combinations of anthracene and hl-phenyl-Z-naphcomponent to give substantially the'saine desired results thylamine and of N-phenyl-Znapthylarmne and pyrene as those achieved with acridine per se. I eifectivel-y retard the oxidation and viscosity changes of It is also to be understood that N-aryl-Z-naphthylamine, tetrakis(1H,1H,wH-polyiluoroall yl) pyromellitate that is such as N o-tOlyLZ-naphthylamine, N-2-naphthyl-2-naphsubjected'to'contact with oxygen at elevated temperatures. thylamine and N-9-anthranyl-2-haphthylamine may be This .polyfluoroalkyl ester has an alkyl group that is a substituted for the N-phenyl-l-naphthylamine of the folmixture of C and C atom chains. On'being oxidized as described above at 572 F. and at 662 F. the results recorded in Table II were obtained.

oxidized with recirculated oxygen are presented in Table Table II OXIDATION or TETRAKIS (1H, wH, kH-POLYFLUOROALKYL) PYROMELLITA'IE [10 ml. ester] A. TEMPERATURE, 572 F.

Oxygen Absorbed Viscosity Change in per- Amt, per cent: Measured Agent Tested cent by Ave. for Ave. for Total at Weight 1st hr., 2nd hr., in 3 rnL/rnin. ml./min. hrs.,

None 2.32 0. G3 170 -31 -28 .tnthracene and N phenyl-2-naphthylamine- 0. 25+. 25 0. 05 08 9 -7 N Pheuyl-2-naphthylan1ine and pyrene 0. 25+O. 25 0.07 .04 8 7 +1 B. TEMPERATURE, 662 F.

None 2. 70 50 186 70 2. N-Phenyl-2-naphthylamine and pyrene- 0. 25+0. 25 .47 17 47 .ni.

EXAMPLE 3 30 Table IV A combination of acridine and pyrene retards the in- OXIDATION OF DC-55U SILICONE 01L crease in viscosity and the corrosion of metals in tetra- [20 ml. sample at572F., oxygen n mL/mirL] butyl pyromellitate through which air is bubbled at 500 F. This oxidation corrosion test is a standard procedure s s y increase (Federal Test Method Standard No. 791, Method 5308.4) Amount Oxygen in percent used for qualifying lubricants under MIL-L-9236 specie t st d P r s l y m in at I fication. The test results are summarized in Table III. Weight hours Table III 100 210 OXIDATION OF TETRABUTYL PYROMELLITATE 40 [100 m1. sample at 500 F., air flow at 83 ml./mi11.] None 97. 4 21 15 Anthracene and N-phenyl-2- Esterplus Anaphthylamine 0.25+0.2 29.4 5-7 3. Control (NO 025% Am? cridme and pyrene 0.25+0- e 15-0 21 added agent) dine and 025%pyrene As many apparently Widely different embodiments of 4;) d this Invention may be made without departing from the pelcem mcmdse measme at 392 7 4 spirit and scope thereof, it is to be underestood that this 0 on invention is not limited to the specific embodiments there- 21% of except as defined in the appended claims.

8.32 +8.8; The embodiments of the invention in which an ex- 0 04 +0104 elusive property or privilege is claimed are defined as o 05 +0. 04 follows:

EXAMPLE 4 Anthracene (0.25 part) and N-phenyl-Z-naphthylamine (0.25 part) added to 100 parts of pentaerythritol tetrapivalate so retards oxidation at 500 F. when oxygen is bubbled through a 10 ml. sample of the ester in the apparatus and by the procedure described for the tests with bis(2-ethylhexyl) sebacate summarized in Table I that only 8 ml. of oxygen are absorbed in three hours whereas the untreated ester absorbs 87 ml. of oxygen in the same time. The viscosity at 100 F. of the treated ester increases from 298 centistokes before oxidation to only 312 centipoises or 5% after the oxidation while the viscosity of the untreated control sample increases to 410 centistokes or 38%.

EXAMPLE 5 The effect of acridine and pyrene in combination and of anthracene and N-phenyl-Z-naphthylamine used together in a methyl phenyl silicone (DC-550 silicone oil) is marked in retarding oxidation at 572 F. and in suppressing an increase in viscosity in the oil. The results of oxidizing the silicone oil as the esterlubes have been 1. A high temperature mechanical fluid selected from the group consisting of esters and silicone oils, said fluid containing an antioxidant composition of a component selected from the group consisting of an N aryl-2- naphthylamine and an acridine, in combination with a polynuclear aromatic hydrocarbon component having at least three fused rings said polynuclear aromatic hydrocanbon being. selected from the group consisting of anthracene, benzanthracene, chrysene and pyrene, the singlet-triplet excitation energy of said hydrocarbon being less than 20,000 cmf each of said antioxidant components being present in an amount within the range of 0.025% to 2.5% by Weight of said mechanical fluid.

2. A high temperature mechanical fluid according to claim 1 wherein the antioxidant composition is a combination of acridine and pyrene.

3. An antioxidant composition for high temperature mechanical fluids selected from the group consisting of esters and silicone oils, said composition consisting of a component selected from the group consisting of an N-aryl-Z-naphthylamine and an acridine, together with a polynuolear aromatic hydrocarbon component having at least three fused rings, said polynuclear aromatic hydrocarbon being selected from the group consisting of anthracene, benzanthnacene, ch-rysene and pyrene, the singlet-triplet excitation energy of said hydrocarbon being less than 20,000 c r the proportion of said components being in equal parts by weight and each of said components being present in an amount to achieve a concentration in said mechanical fiuid within the range of 0.025% to 2.5% by Weight of said fluid. 4. An antioxidant composition according to claim and pyrene.

References Cited in the file of this patent UNITED STATES PATENTS Fischer et a1. Apr. 18,

Dow July 18,

Musher Jan. 25,

Diamond Sept. 23,

FOREIGN PATENTS Great Britain Feb. 25,

France May 8, 

1. A HIGH TEMPERATURE MECHANICAL FLUID SELECTED FROM THE GROUP CONSISTING OF ESTERS AND SILICONE OILS, SAID FLUID CONTAINING AN ANTIOXIDANT COMPOSITION OF A COMPONENT SELECTED FROM THE GROUP CONSISTING OF AN N - ARYL-2NAPHTHYLAMINE AND AN ACRIDINE, IN COMBINATION WITH A POLYNUCLEAR AROMATIC HYDROCARBON COMPONENT HAVING AT LEAST THREE FUSED RINGS SAID POLYNUCLEAR AROMATIC HYDROCARBON BEING SELECTED FROM THE GROUP CONSISTING OF ANTHRACENE, BENZANTHRACENE, CHRYSENE AND PYRENE, THE SINGLET-TRIPLET EXCITATION ENERGY OF SAID HYDROCARBON BEING LESS THAN 20,000 CM-1, EACH OF SAID ANTIOXIDANT COMPONENTS BEING PRESENT IN AN AMOUNT WITHIN THE RANGE OF 0.025% TO 2.5% BY WEIGHT OF SAID MECHANICAL FLUID. 